There are presently several methods of achieving bistable operation. Descriptions of their operational methods are as follows:
A--Latching Method:
1--Two relays are mounted adjacently, each having a latching bar that engages with each other. When relay "A" is energized, the latch bar locks up relay "B" in a non-energized mode, and remains that way whether power to relay "B" is maintained or removed. Conversely, when relay "B" is energized, the latch bar locks up relay "A" in a non-energized mode, and remains that way whether power to relay "B" is maintained or removed.
B--Detent Method:
1--In a detent type, a single relay is used with the armature engaged to a split point detent which has a lateral motion to one side or the other with each full excursion of the armature. When the relay is energized, the excursion of the armature moves the detent to one side and it remains in that position. When the power to the relay is released and then re-energized, the excursion of the armature moves the detent to the other side, and it remains in that position. Each time the relay is energized, the detent alternates and holds from one side to the other. By means of a linkage or of an actuating arm or of an eccentric cam, the alternate motion of the detent is used to make or release contacts on the relay.
C--Ratchet and Pawl Method:
In this method, a single relay is used. The armature is involved directly, or through linkage to a pawl which engages a ratchet gear on a shaft. When the relay is energized, the excursion of the armature can be made to either cause a rotation of the shaft, or the rotation of the shaft can occur when the relay is de-energized. By means of alinkage or of an actuating arm or of a cam, the rotation of the ratchet shaft is used to maintain contacts in a make or non-make mode each time the relay is energized or de-energized.
D--Magnetic Method:
1--Magnetic types can be made in single relay or dual relay operation. In the single relay version, a permanent magnet is mounted on the pole piece. The magnetic force of the magnet is sufficient to maintain the armature in an energized position once the relay is energized, but has insufficient magnetic force to energize the relay on its own. In operation, full DC power is supplied to the relay coil to seat the armature. When power is removed, the magnet retains the armature in a seated position, and holds the contacts in a make mode. To release the armature, DC voltage is applied in reverse polarity and at a critical power level that is just sufficient to overcome only the magnetic hold of the magnet, so that the armature releases and the contacts return and hold in a non-make mode.
2--In the magnetic two relay type, two relays face each other with a permanent magnet bar interface having sufficient magnetic force to hold a pivoted common armature for each relay in an energized position on the relay that is energized. The single armature is pivoted between each relay so that when one side of the armature closes on one relay, it will open on the other relay. When sufficient power is applied to one relay coil, the armature will close and remain closed on that relay by the magnetic force of the permanent magnet even when power is removed. When sufficient power is applied to the second relay, the armature will close on the second relay and release the armature of the first relay and the second relay will remain and hold in closed position by the magnetic force of the permanent magnet, even if the power is removed. The rocking motion of the armature due to the closing and opening of each relay is made use of by means of shaft, linkage or operating arm to alternately hold the contacts in either a make or a non-make mode.
E--Electronic Method:
1--The electronic type uses solid state circuitry to place a relay in a make or non-make (release) mode. The circuitry usually consists of integrated circuits (I.C.'s) and/or transistors (PNP's, NPN's, and/or SCR's, etc.) depending on the design. In electronic units, applied power remains on at all times to supply the circuitry, and the make or non-make mode of the relay is controlled and alternated by each opening or each closing of an external control switch, which is applied to the control circuitry of the relay. In the opening switch type, with power applied, the closing of the external switch causes no change in the initial mode of the relay, which is in a non-energized state. Upon opening of the external switch, the relay becomes energized and remains in that state until the external switch is again closed, and then re-opened at which time the relay returns to the non-energized state and remains in that state until the aforegoing cycle of the external switch is repeated.